1. Field of the Invention
The present invention relates to an optical image stabilizer to be used for optical apparatuses such as video cameras and interchangeable lenses.
2. Description of the Related Art
Optical image stabilizers are operable to move (shift) an image stabilizing lens that constitutes part of an image capturing optical system or an image sensor that photoelectrically converts an object image formed by the image capturing optical system in directions orthogonal to an optical axis of the image capturing optical system in response to a shake of an optical apparatus to correct (or reduce) image blur caused by the shake of the optical apparatus. The shake of the optical apparatus is detected by a shake detector such as an angular velocity sensor provided in the optical apparatus. Shift drive of the image stabilizing lens or the image sensor enables correction of the image blur. The image stabilizing lens and the image sensor are hereinafter collectively referred to as “an image stabilizing element”.
Japanese Patent Laid-Open No. 2010-139694 discloses one of such optical image stabilizers which determines whether or not magnitude of the shake exceeds a predetermined level and whether or not panning is being performed and which changes a movable amount of the image stabilizing element according to a result of the determination. Specifically, this optical image stabilizer sets a larger movable amount in a case where the magnitude of the shake exceeds the predetermined level and the panning is not being performed as compared with other cases. Accordingly, the optical image stabilizer sets such a larger movable amount of the image stabilizing element in a case where the magnitude of the shake is large because a user performs image capturing while walking as compared with a case where the user performs image capturing in a resting state, thereby improving image stabilization performance. On the other hand, the optical image stabilizer sets a smaller movable amount of the image stabilizing element in a case where the user performs image capturing with panning as compared with the case where the user performs image capturing while walking, thereby avoiding deterioration of image quality due to a large shift of the image stabilizing element during the image capturing with panning.
However, the optical image stabilizer disclosed in Japanese Patent Laid-Open No. 2010-139694 may determine that, when fast panning is performed, a shake is generated not due to the panning, but due to the walking, and therefore may set a large movable amount of the image stabilizing element.
FIG. 7A shows an example of a shake detection signal (angular velocity signal) showing a shake of an optical apparatus used while a user is walking. In FIG. 7A (and FIGS. 7B and 7C), a vertical axis shows value of the shake detection signal (angular velocity ω) and a horizontal axis shows time t. FIG. 7A shows a state where the user is not walking until a time TW1 and a state where the user is walking from the time TW1 to a time TW2. FIG. 7A further shows, after the time TW2, a state where the user is not walking again. When the user starts walking at the time TW1, the value of the shake detection signal exceeds a predetermined value V1, and thereafter a polarity (sign) of the shake detection signal reverses and the value thereof exceeds a predetermined value −V1. While the user is walking, the polarity of the shake detection signal alternately reverses and the values thereof exceeding the predetermined values V1 and −V1 are output.
FIG. 7B shows an example of the shake detection signal when slow panning is performed. The panning is started at a time TP1, and the panning is ended at a time TP2. When the slow panning is performed, the value of the shake detection signal exceeds the predetermined value V1, but the polarity thereof does not alternately reverse, which makes it possible to distinguish a shake generated by the slow panning from a shake generated during the walking.
FIG. 7C shows an example of the shake detection signal when fast panning is performed. The fast panning is often performed so as to pass over an object once and then return to the object again. After the fast panning is started at a time TP3, the value of the shake detection signal exceeds the predetermined value V1. Then, the panning is performed so as to pass over the object once at a time TP4, is reversed in direction to return to the object and is thereafter ended at a time TP5.
In image capturing while such fast panning is performed, the polarity of the shake detection signal reverses after the value thereof exceeds the predetermined value V1 and then the value thereof exceeds the predetermined value −V1, which may cause erroneous detection that the image capturing with fast panning is determined as the image capturing while walking. Such erroneous detection causes setting of a larger movable amount of the image stabilizing element than a movable amount that should be set small during the image capturing with fast panning, which deteriorates image quality due to a large shift of the image stabilizing element during the image capturing with fast panning.